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M Arnold

Publications and source records attributed to M Arnold.

At least 91 records · Page 5Linked to original sources
PubMed1999

Time-variant spectral analysis of LDF signals on the basis of multivariate autoregressive modelling.

Time-variant AR-modelling was used to analyse the non-stationary properties of LDF signals during provocation tests. The procedure for the estimation of time-varying AR parameters based on Kalman filtering is presented. The estimates can be used to calculate instantaneous measures, such as peak frequency, spectral band power and coherence. The resulting course of instantaneous peak frequency of a sinusoidal signal with frequency jump was compared to similar parameters derived from short-time FFT and Hilbert transformation. Univariate time-variant spectral analysis was used to investigate LDF measurements in patients with Raynaud's phenomena. The experimental protocol was splitted into phases of different room temperature. The results demonstrate time-dependent variations of spectral components (amplitude and frequency). By means of time-variant coherence analysis of LDF and diameter measurements of vessels in a hamster skin fold the existence of a main rhythm around 0.1 Hz in the LDF signals which is related to vasomotion is shown.

Algorithms↗
PubMed1999

3D-visualization improves the dry-lab coronary anastomoses using the Zeus robotic system.

BACKGROUND: Robotic surgical instruments enable quick and precise movements and may allow complete endoscopic coronary artery bypass grafting. However, cardiac surgeons will have to become familiar with this technology and endoscopic viewing. We present our training program with special focus on 2D- and 3D-visualization. METHODS: A thoracic skeleton, covered with a neoprene suit, served as model for the chest wall. Either a glove, fixed on a metal plate, or a pig heart were placed inside for training. On the glove, a suture line consisting of two lines of 16 points each, with a distance of 2 mm between each point, was stamped. On the pig heart, the LAD was prepared and incised; subsequently an anastomosis was done using the dissected right coronary artery as a graft. The time required was measured for both models. For suturing, the Zeus System (Computer Motion, Goleta, CA) was used and the third robotic arm positioned the endoscopic camera. The scopes were connected to a 3D-camera and the picture was displayed on a headset with two integrated monitors. Visualization was set to either 2D or 3D. Three surgeons were involved in the study. Each one did at least 12 anastomoses on 2D and 3D. RESULTS: The three surgeons involved showed a clear and rapid learning curve. The times required for the suture line decreased from 12.5 +/- 1.6 to 8.5 +/- 0.5 minutes with 2D and from 11.9 +/- 5.4 to 7.8 +/- 0.5 minutes for 3D respectively. This decrease did reach statistical significance (p = 0.03). In the pig heart model, the anastomosis times decreased from 33.2 +/- 8.4 to 15.7 +/- 0.3 minutes with 3D-visualization, and from 36.2 +/- 2.2 to 29.5 +/- 3.3 minutes with 2D. The decrease in anastomosis time did again reach significance (p = 0.025). At the end of the study, the times achieved with 2D-visualization were significantly longer than those with 3D (p = 0.01). CONCLUSIONS: A surgical training program is mandatory to become familiar with these new technologies. Both models showed learning curves over an acceptable time course. 3D-visualization facilitated quick and precise movements, thus resulting in shorter anastomosis times.

Anastomosis, Surgical↗
PubMed1998

Sequence and mutational analysis of the devBCA gene cluster encoding a putative ABC transporter in the cyanobacterium Anabaena variabilis ATCC 29413.

The devBCA gene cluster (dev for development), shown to be essential for envelope formation in heterocysts of Anabaena sp. strain PCC 7120, was identified in the gene bank of a second heterocyst-forming strain, Anabaena variabilis ATCC 29413. Sequence and structural organization of the three genes, encoding subunits of a presumptive ABC transporter, were nearly identical in both strains. Mutants of A. variabilis defective in the devA gene were constructed. As devA mutants of Anabaena 7120, A. variabilis mutants were unable to grow on N2 as sole nitrogen source due to incomplete differentiation of heterocysts.

ATP-Binding Cassette Transporters↗
PubMed1998

Nosology

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Journal Article↗
PubMed1998

Lipopolysaccharide-induced anorexia following hepatic portal vein and vena cava administration.

To examine the role of the liver in lipopolysaccharide (LPS)-induced hypophagia, we investigated the effect of hepatic portal and vena cava infusions (1 mL/30 min) of LPS (100 microg/kg of body weight) on feeding in rats. LPS infusion significantly reduced food intake when administered via either the hepatic portal vein or the vena cava. Both the magnitude and time course of this hypophagia were similar regardless of the infusion route. As in previous experiments of ours in which LPS was administered by intraperitoneal (i.p.) injection, LPS reduced food intake by decreasing meal frequency, without affecting meal size or duration. The results suggest that peripherally administered LPS does not act primarily in the liver to reduce food intake.

Animals↗
PubMed1998

Radiation-induced impairment of bone healing in the rat femur: effects of radiation dose, sequence and interval between surgery and irradiation.

BACKGROUND AND PURPOSE: Impairment of osseous healing in treatment combining surgery and radiotherapy is a frequent complication. Its dependence on sequence and interval was studied in a defined experimental model. MATERIALS AND METHODS: The effect of pre- and postoperative irradiation by single doses of X-rays on osseous closure of a 1.2 mm drill hole in the rat femur was measured 6 or 7 weeks after surgery in histological sections using morphometrical methods. RESULTS: Irradiation delivered between 1 day and 6 months before surgery resulted in a reduction of bone healing following very similar dose response relationships; there was no evidence of any slow repair of latent radiation damage. Radiosensitivity of bone healing during the first 3 days after surgery was not different from preoperative irradiation; however, irradiation 4 days or later after surgery failed to reduce osseous healing even after very high radiation doses. CONCLUSION: Tolerance increases enormously if radiotherapy is given later than 4 days after surgery. This has great implications for combined radiotherapy and surgery schedules involving bone reconstruction, but may be even more important for radiotherapy applied to prevent heterotopic ossification after total hip arthroplasty. Biologically, target cell regeneration alone is insufficient to account for the drastic rise in radiotolerance; it must be accompanied by an increase in cellular resistance due to differentiation.

Animals↗
PubMed1998

Quantification and rejection of ocular artifacts in auditory evoked fields in schizophrenics.

RESULTS: In a magnetoencephalographic investigation of the auditory evoked field (AEF) in 17 schizophrenics and 17 controls, 37% of the schizophrenics and 12% of the controls showed eye artifacts in every second trial or even more frequently. In the uncorrected average fields, the ratio between the power of artifacts and the power of the magnetoencephalogram (MEG) exceeded the value of 0.1 for 48% of the schizophrenics and for 29% of the controls. Ocular artifacts biased the locations of equivalent current dipoles of the M100 component towards deeper positions. A regression algorithm for the correction of ocular artifacts in raw data and an identification technique of ocular artifacts based on the topography of transmission coefficients is described. CONCLUSIONS: A linear dependence of ocular artifacts in AEF on the electrooculogram (EOG) was confirmed. Possible errors introduced by the correction are discussed. Transmission coefficients should be calculated for several individual trials with the same type of artifact. Errors due to evoked potentials in the EOG were found to be comparable in amplitude to noise in the AEF. Examples of transmission coefficients from the EOG to the MEG are given.

Adult↗
PubMed1998

The DevBCA exporter is essential for envelope formation in heterocysts of the cyanobacterium Anabaena sp. strain PCC 7120.

The gene devA of the filamentous heterocyst-form-ing cyanobacterium Anabaena sp. strain PCC 7120 encodes a protein with high similarity to ATP-binding cassettes of ABC transporters. Mutant M7 defective in the devA gene is arrested in the development of heterocysts at an early stage and is not able to fix N2 under aerobic conditions. The devA gene is differentially expressed in heterocysts. To gain a better understanding of the structural components of this putative ABC transporter, we determined the complete nucleotide sequence of the entire gene cluster. The two additional genes, named devB and devC, encode proteins with similarities to membrane fusion proteins (DevB) of several ABC exporters and to membrane-spanning proteins (DevC) of ABC transporters in general. Site-directed mutations in each of the three genes resulted in identical phenotypes. Heterocyst-specific glycolipids forming the laminated layer of the envelope were identified in lipid extracts of M7 and in the site-directed mutants. However, transmission electron microscopy revealed unequivocally that the glycolipid layer is missing in mutant M7. Ultrastructural analysis also confirmed a developmental block at an early stage of differentiation. The results of this study suggest that the devBCA operon encodes an exporter of glycolipids or of an enzyme that is necessary for the formation of the laminated layer. The hypothesis is proposed that an intact envelope could be required for further heterocyst differentiation.

ATP-Binding Cassette Transporters↗
PubMed1998

Nonlinear dynamics of 3 Hz spike-and-wave discharges recorded during typical absence seizures in children.

One-channel routine recordings of the scalp electroencephalogram (EEG) from unmedicated children strictly classified as unprovoked typical (3 c/s) absence seizures were selected. The dynamics of spike-and-wave discharges (SWD) were then examined by means of autocorrelation, correlation dimension, averaged pointwise dimension and largest Lyapunov exponent. For one EEG signal with pronounced spike-and-wave (SW) patterns, these measures were used complementary to a surrogate data method, a nonlinear (SETAR) modeling approach, and a SW simulation procedure providing five types of SW test signals. The SETAR model exhibited stationary SW dynamics, visually very similar to the EEG target signal, and with clear nonlinear structure. According to the results, the EEG episodes investigated represent low-dimensional dynamics, possibly recorded during nonstationary periods. Arguments that justify the assumption of deterministic chaos in our EEG signals were not obtained with the current methods. From the results one may conclude that two global oscillatory modes are present for the model, and three modes are active during the EEG recording period.

Algorithms↗
PubMed1998

Adaptive AR modeling of nonstationary time series by means of Kalman filtering.

An adaptive on-line procedure is presented for autoregressive (AR) modeling of nonstationary multivariate time series by means of Kalman filtering. The parameters of the estimated time-varying model can be used to calculate instantaneous measures of linear dependence. The usefulness of the procedures in the analysis of physiological signals is discussed in two examples: First, in the analysis of respiratory movement, heart rate fluctuation, and blood pressure, and second, in the analysis of multichannel electroencephalogram (EEG) signals. It was shown for the first time that in intact animals the transition from a normoxic to a hypoxic state requires tremendous short-term readjustment of the autonomic cardiac-respiratory control. An application with experimental EEG data supported observations that the development of coherences among cell assemblies of the brain is a basic element of associative learning or conditioning.

Adaptation, Physiological↗
PubMed1998

TNF-alpha tolerance blocks LPS-induced hypophagia but LPS tolerance fails to prevent TNF-alpha-induced hypophagia.

To investigate the role of tumor necrosis factor-alpha (TNF-alpha) in bacterial lipopolysaccharide (LPS)-induced hypophagia, we tested whether a cross tolerance between LPS and TNF-alpha exists with respect to their anorectic effects. Only the first of three subsequent intraperitoneal injections of LPS (100 micrograms/kg body wt) given every second day at dark onset (12:12-h light-dark cycle) led to a significant reduction of food intake in male rats. Likewise, intraperitoneal injections of human recombinant TNF-alpha (150 micrograms > or = 3 x 10(6) U/kg body wt) also resulted in tolerance to its hypophagic effect. LPS tolerance did not alter the hypophagic response to subsequently injected TNF-alpha (n = 14). However, TNF-alpha pretreatment completely blocked the hypophagic response to LPS (n = 14). The results demonstrate that tolerance to the hypophagic effect of exogenous TNF-alpha is sufficient to eliminate LPS-induced hypophagia. This is consistent with the hypothesis that endogenous TNF-alpha plays a major role in LPS-induced hypophagia. The ineffectiveness of LPS tolerance to attenuate TNF-alpha-induced hypophagia is compatible with findings demonstrating that reduced TNF-alpha production is an important feature of LPS tolerance.

Animals↗
PubMed1998

A rapid assay for tyrosine hydroxylase activity, an indicator of chronic stress in laboratory and domestic animals.

Tyrosine hydroxylase (TH) (EC 1.14.16.2) activity has been frequently employed as a marker of adrenomedullar catecholamine-synthesizing capacity and, thus, as an indicator of chronic stress exposure in various animal species. We have developed a thin layer chromatography (TLC) procedure for its assay in adrenal glands of rats and large animals that reduces some of the drawbacks of currently employed methods, thereby facilitating routine use. Preparation of tissue samples was adapted for rats and pigs. The activity of the enzyme is expressed as the rate of the TH-catalysed tyrosine hydroxylation to 3,4-dihydroxyphenyl-alanine (DOPA) using tritium-labeled tyrosine, in the presence of cofactors and a DOPA decarboxylase inhibitor. The subsequent separation of the radioactive product (DOPA) from the substrate (tyrosine) is accomplished by TLC on silicagel plates, in a n-butanol/acetic acid/water solvent system (4:1:1). Radioactivity in the scraped zones, in which DOPA has been detected by means of an internal standard, is measured by beta-counting. An advantage of this procedure is its simplicity, reliability, and convenience for routine assays. Levels of endogenous adrenal tyrosine (HPLC assay) are considerably higher in pig (2.5-5 nmol/mg protein) than in rat (0.15 nmol/mg protein); their effects upon assay results being, in both cases, negligible. Michaelis constants estimated by this procedure amounted to 0.9 mmol l(-1) (at 0.7 mM DMPH4) for pig, and 1.1 mmol l(-1) (at 1.5 mM DMPH4) for rat.

Adrenal Medulla↗
PubMed1998

Multimodal time-variant signal analysis of neonatal EEG burst patterns.

It can be shown that dominant rhythmic signal components of neonatal EEG burst patterns (discontinuous EEG in quiet sleep) are characterized by a quadratic phase coupling (bispectral analysis), i.e. a multiplicative interaction (connection) between the underlying electrophysiological processes can be assumed. By means of pattern recognition algorithms as well as time-variant spectral and coherence analysis, a so-called "initial wave" (narrow band rhythm within a frequency range of 3-12 Hz) can be demonstrated within the first part of the burst pattern. The detection of this signal component and of the quadratic phase coupling is more successful in the frontal region. By means of amplitude demodulation of the "initial wave" the phase coupling can be attributed to an amplitude modulation. The results were derived from 6 neonates (20 burst patterns for each neonate; 8-channel recordings). A 16-channel EEG-recording was analyzed for one neonate.

Electroencephalography↗
PubMed1997

Analysis of the interrelations between a low-frequency and a high-frequency signal component in human neonatal EEG during quiet sleep.

It can be shown that dominant rhythmic signal components of neonatal EEG burst patterns (discontinuous EEG in quiet sleep) are characterised by a quadratic phase coupling (bispectral analysis). A so-called 'initial wave' (narrow band rhythm within a frequency range of 3-12 Hz) can be demonstrated within the first part of the burst pattern. The detection of this signal component and of the phase coupling is more successful in the frontal region. By means of amplitude demodulation of the 'initial wave' and a subsequent coherence analysis the phase coupling can be attributed to an amplitude modulation, i.e. the envelope curve of the 'initial wave' shows for a distinct period of time the same qualitative course as the signal trace of a 'lower' frequency component (0.75-3 Hz). The results were derived from six neonates (20 burst patterns for each neonate; 8 channel recordings).

Brain Mapping↗
PubMed1997

Simultaneous spike detection and topographic classification in pediatric surface EEGs.

In this study, an algorithm is introduced for the automatic detection and simultaneous topographic classification of interictal regional spike activity in pediatric surface EEG records. The algorithm is based on the classification of the topographic distribution of instantaneous power by means of a 'group' trained classifier. The results of automatic spike analysis were compared with the decisions of two experienced electroencephalographers. Four routine EEG records exhibiting (multi)regional spikes were examined. The mean selectivity for the automatic spike detector was 84.6% (mean sensitivity 88.1%, mean specificity 89.3%) and for the electroencephalographers 85.3%. All spikes detected by the algorithm were simultaneously classified according to their topographic characteristics. The results of automatic spike classification (lateralization/localization) corresponded to the results of visual analysis.

Algorithms↗
PubMed1997

Bacterial degradation of styrene in waste gases using a peat filter.

A biofiltration process was developed for styrene-containing off-gases using peat as filter material. The average styrene reduction ratio after 190 days of operation was 70% (max. 98%) and the mean styrene elimination capacity was 12 g m-3 h-1 (max. 30 g m-3 h-1). Efficient styrene degradation required addition of nutrients to the peat, adjustment of the pH to a neutral level and efficient control of the humidity. Maintenance of the water balance was easier in a down-flow than in an up-flow process, the former consequently resulting in much better filtration efficiency. The optimum operation temperature was around 23 degrees C, but the styrene removal was still satisfactory at 12 degrees C. Seven different bacterial isolates belonging to the genera Tsukamurella, Pseudomonas, Sphingomonas, Xanthomonas and an unidentified genus in the gamma group of the Proteobacteria isolated from the microflora of active peat filter material were capable of styrene degradation. The isolates differed in their capacity to decompose styrene to carbon dioxide and assimilate it to biomass. No toxic intermediate degradation products of styrene were detected in the filter outlet gas or in growing cultures of isolated bacteria. The use of these isolates in industrial biofilters is beneficial at low styrene concentrations and is safe from both the environmental and public health points of view.

Biodegradation, Environmental↗